Computer software application programs, during execution and installation, make use of a variety of native resources provided by the operating system of a computer. A traditional, single-user computer is depicted in FIG. 1A. As shown in FIG. 1A, native resources provided by the operating system 100 may include a file system 102, a registry database 104, and objects 106. The file system 102 provides a mechanism for an application program to open, create, read, copy, modify, and delete data files 150, 152. The data files 150, 152 may be grouped together in a logical hierarchy of directories 160, 162. The registry database 104 stores information regarding hardware physically attached to the computer, which system options have been selected, how computer memory is set up, various items of application-specific data, and what application programs should be present when the operating system 100 is started. As shown in FIG. 1A, the registry database 104 is commonly organized in a logical hierarchy of “keys” 170, 172 which are containers for registry values. The operating system 100 may also provide a number of communication and synchronization objects 106, including semaphores, sections, mutexes, timers, mutants, and pipes. Together, the file system 102, registry database 104, objects 106, and any other native resources made available by the operating system 100 will be referred to throughout this document as the “system layer” 108. The resources provided by the system layer 108 are available to any application or system program 112, 114.
A problem arises, however, when execution or installation of two incompatible application programs 112, 114 is attempted. As shown in FIG. 1A, two application programs, APP1 112 and APP2 114, execute “on top of” the operating system 100, that is, the application programs make use of functions provided by the operating system to access native resources. The application programs are said to be incompatible with one another when they make use of native resources 102, 104, 106 in a mutually exclusive manner either during execution or during the installation process. APP1 112 may require, or attempt to install, a file located by the pathname c:\windows\system32\msvcrt.dll and APP2 114 may require, or attempt to install, a second, different file that is located by the same pathname. In this case, APP1 112 and APP2 114 cannot be executed on the same computer and are said to be incompatible with one another. A similar problem may be encountered for other native resources. This is, at best, inconvenient for a user of the computer who requires installation or execution of both APP1 112 and APP2 114 together in the same operating system 100 environment.
FIG. 1B depicts a multi-user computer system supporting concurrent execution of application programs 112, 114, 112′, 114′ on behalf of several users. As shown in FIG. 1B, a first instance of APP1 112 and a first instance of APP2 114 are executed in the context of a first user session 110, a second instance of APP1 112′ is executed in the context of a second user session 120, and a second instance of APP2 114′ is executed in the context of a third user session 130. In this environment, a problem arises if both instances of APP1 112, 112′ and both instances of APP2 114, 114′ make use of native resources 102, 104, 106 as if only a single user executes the application. For example, the APP1 112 may store application specific data in a registry key 170. When the first instance of APP1 112 executing in the first user context 110 and the second instance of APP1 112′ executing in the second user context 120 both attempt to store configuration data to the same registry key 170, incorrect configuration data will be stored for one of the users. A similar problem can occur for other native resources.
The present invention addresses these application program compatibility and sociability problems.